A wind turbine generator may be mounted in a nacelle which is mounted on top of a wind turbine tower. In the nacelle, a rotor shaft at which plural rotor blades are connected may be supported and the rotor shaft may be mechanically connected to a generator rotor which may comprise plural permanent magnets and which may rotate relative to a stator portion of the generator mounted within the nacelle. During operation of the generator, voltages and currents may be induced in the stator winding due to an induction effect which is caused by the rotation of the permanent magnets relative to stator windings. Thereby, during operation of the generator, the temperature of the generator may increase. Therefore, typically, during operation of the generator it is necessary to cool the generator, in particular a direct drive generator in which the generator rotor is directly connected to the rotor shaft of the wind turbine, at which the plural rotor blades are mounted.
Conventionally, a liquid link system may be used, in order to cool a direct drive wind turbine, in particular a direct drive generator. However, when using a liquid link system, the cooling air temperatures may be approximately 20 degrees higher than when using a direct cooled generator or using a direct cooling system. Further, the liquid link system may be relatively complicated and expensive.
A direct cooling system may be less expensive than a liquid link cooling system. Reducing the temperature of the generator may enable to increase the torque generated by the wind up to 5%. The advantage of the liquid link system may be that little air is exchanged with the surroundings, thus reducing the corrosion levels in the generator. With the liquid link it may also be easier to keep the humidity at a level which is relatively low. Summarizing, a liquid link system may give little dirt entering the generator and low humidity for reduced corrosion issues.
The conventional direct cooling systems have some disadvantages, in particular regarding reliability of the operation of the generator or reliability and safety of the operation of the cooling system.
Thus, there may be a need for an arrangement and a method for cooling a generator mounted in a nacelle of a wind turbine, which is reliable, safe and may ensure a proper operation for a relatively long time, thus reducing maintenance efforts and costs.
This need may be solved with the subject-matter of the independent claims.